Solar thermal energy array and drive

ABSTRACT

Disclosed are systems and methods for controlling arrays of solar thermal energy collectors. Rows of the array are actuated sequentially or consecutively rather than concurrently.

This application is a continuation application of application numberPCT/US2009/004146, filed Jul. 16, 2009, entitled “Solar Thermal EnergyArray and Drive,” inventors K. Nakasato et al., and published asWO2010/008584, and this application also claims the benefit of priorityto U.S. App. Ser. No. 61/135,146 filed Jul. 16, 2008 and entitled“SopoTracker”, each of which is incorporated by reference herein in itsentirety as if put forth in full below.

FIELD OF THE INVENTION

The invention relates to solar thermal energy arrays, such as solarthermal trough arrays for collecting solar thermal energy.

BACKGROUND AND BRIEF SUMMARY OF THE INVENTION

Solar thermal energy collectors are often installed as arrays having aplurality of collector rows. Each row may be formed of a plurality ofindividual collectors, such that the array resembles a traditional arrayof cells arranged in columns and rows.

Tracking systems for solar thermal energy collectors enable thecollectors to move to track apparent motion of the sun across the sky.Each collector in an array may be controlled individually to provideaccurate tracking in a centralized control configuration, and thereforeeach individual collector in a “cell” of a row may be controlledindividually so that each may separately track the sun's apparentmovement to collect solar energy. Often, each collector movescontinuously using a slow—but constantly—moving drive system.

The invention in one instance provides a solar thermal energy collectorarray which has a column comprising a plurality of adjacent solarthermal energy cells in which the individual cells each share a singlerow controller. Two, three, four, five, six, seven, eight, nine, ten, ormore of these cells may share a single controller.

A cell in this instance may be a single solar thermal energy collectoror may be a plurality of solar thermal energy collectors whose collectortubes are in fluid communication with one another, so that the workingfluid passing through a first collector of the cell subsequently passesthrough a second collector of the cell to be heated further. A cell maytherefore have two, three, four, five, six, seven, eight, nine, ten,twelve, fourteen, sixteen, or more collectors in a given row that areactuated by a single row controller.

The central controller may be configured so that the row controllers areactuated sequentially so that e.g. the first cell moves then remainsstationary, the second cell moves then remains stationary, the thirdcell moves then remains stationary, and so forth until the last cell hasbeen moved and the cycle repeats.

Alternatively, the controller may be configured to actuate rowcontrollers consecutively but not in order so that e.g. the first cellmoves then remains stationary, the third cell moves then remainsstationary, the fifth cell moves then remains stationary, and so forthuntil the last cell in the column has been moved and a second part ofthe cycle begins with the second cell moving, followed by the fourthcell, etc.

There may be arrays adjacent to one another which form a complex array.Therefore, there may be plural row controllers arranged adjacent to oneanother in a row of the complex array. The row controllers in a row maybe programmed identically or not. The row controllers in a row may besynchronized or not. The heated working fluid from one part of the rowof the complex array may or may not be fed to the adjacent part of therow in the complex array.

The row controllers in a complex array may therefore be configured tooperate independently of one another. Alternatively, plural adjacent rowcontrollers such as two, three, four, or more adjacent row controllersmay be configured to operate together.

Row controllers may be intelligent, stand-alone controllers that do notcommunicate with other controllers. Thus, in one configuration, each ofthe controllers is a stand-alone controller that receives various inputsand provides control outputs to the rows for which the controller isconfigured.

Row controllers configured as discussed above may be arranged in adistributed control system in which one or more control centers havinge.g. a programmable logic controller, microprocessor, microcontroller,or computer communicates with each of the row controllers. In thisinstance, the row controllers do not stand alone and, instead, depend onthe control center or centers for some information used to control therows associated with that row controller.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts rays parallel to the axis of symmetry reflecting to thefocus of the parabola.

FIG. 2 illustrates a field of collectors consisting of rows orientedalong the north-south longitude. Each trough collector rotates aroundthe absorber tube to adjust the east-west orientation of the collector.

FIG. 3 shows an organization of controllers used to enable both large,field-level and small, row-specific commands. In the diagram,connections are labeled as “switches,” but routers may also be used tofacilitate communication between controllers.

FIG. 4 illustrates an 18-inch sprocket as part of the chain-sprocketapparatus that rotates the collector row.

FIG. 5 shows a box containing an optical encoder, which sends thecollector position to the Row Controller hardware.

FIG. 6 illustrates Row Tracker hardware which has a printed circuitboard, CPU, motor power supply, and a 5- and 12-volt power supply.

FIG. 7 depicts a single board computer, which is programmed with thesoftware to operate the collectors.

FIG. 8 illustrates one array of the invention with local control, withthe row controller in the immediate vicinity of rows controlled by therow controller as opposed to being positioned at a more remote locationsuch as a control room or periphery of a complex array.

FIG. 9 illustrates a complex array having four arrays, each with its rowcontroller positioned in the immediate vicinity of rows controlled bythe respective row controllers.

FIG. 10 depicts a control strategy for arrays of FIG. 8 and FIG. 9.

FIG. 11 illustrates one array of the invention with distributed control,where a row controller in the immediate vicinity of rows controlled bythe row controller receives setpoints from a more remote, centralcontroller such as a field controller.

FIG. 12 and FIG. 13 illustrate complex arrays comprising e.g. four ofthe arrays of FIG. 11.

FIG. 14 depicts a control strategy for arrays of FIG. 11-13.

ADDITIONAL SUMMARY AS WELL AS MORE DETAILED DESCRIPTION, INCLUDING BESTMODE

There are a number of ways to track the apparent movement of the sun.

One way is to use or develop tables or data of the sun's position orutilize an equation that calculates the sun's position as a function ofthe time of day and day of year for the latitude at which the collectorarray is located. The time of day may be obtained from a clock withinthe controller, from a website on the World Wide Web, or from a radiotransmission of time from e.g. a national bureau. Alternatively, tablesthat contain or equations that generate data representing the angle atwhich solar collectors of a row would ideally be positioned may beutilized.

Another way is to utilize global positioning satellite (GPS) data toassess the geographic position of an array or part of a complex array ofcollectors to calculate the angle of the sun and optionally obtain thetime of day provided as part of a typical GPS signal. This data isuseful in calculating the angle at which the collectors of a row of anarray should be positioned.

Data as obtained above may be used to position and control solar thermalenergy collectors. Alternatively, data as obtained above may be modifiedand used to position collectors to compensate for inaccuracies ofmeasurement or movement.

One inaccuracy that may exist when comparing actual position of a solarthermal energy collector and theoretical position as obtained above ismisalignment of an inclinometer used to provide a signal indicative ofthe angle at which the collector is positioned. It can be quitedifficult to position an inclinometer at exactly the position it shouldbe positioned during installation. One way to compensate formisalignment of the inclinometer is to measure the difference betweenthe theoretical position and the position at which a collector rowprovides the greatest illumination of its collector tube and store thisinformation for each collector or row as an “alignment offset” that maybe added to or subtracted from the theoretical angle to provide a rowcontroller set point. This modified set point may be calculated at therow controller, or the modified set point may be calculated at a centralcontroller.

Another inaccuracy that may exist when comparing actual position andtheoretical position for a collector is due to wear over time. Wear maybe compensated for by incorporating a wear offset either directly intothe alignment offset by adding it to or subtracting it from the storedalignment offset and storing the new number or by storing the wearoffset separately in a database and adding to or subtracting from themodified set point above.

The alignment offset and wear offset may be measured manually, or theseoffsets may be calculated by providing alignment equipment in the solararray. For example, a collector tube of a row may have a brightnessmeter attached that indicates brightness of light shining on the tube.The row controller may periodically move the collector row to determinethe position at which maximum brightness occurs and calculate either anew alignment offset or a new wear offset value that may be stored in adatabase.

Another source of inaccurate alignment is wind pressure on collectors ofa row. A row of solar thermal energy collectors that are interconnectedto rotate synchronously have a large surface area against which windapplies pressure. There are a number of ways to compensate for windpressure.

One is to use information obtained from an on-site weather station thatprovides data about wind speed and direction to calculate a windpressure offset. This value may be stored or may be calculatedconstantly to provide an offset value added to or subtracted from othervalues as discussed above to correct for current wind conditions.

Another way to compensate for wind pressure is to compare the collectorrow angle set point with either an instantaneous reading from theinclinometer or a time-averaged reading for a period of time during theday (e.g. the preceding five or ten minutes) as well as compare to windspeed and direction to calculate a wind pressure offset that can be usedto adjust the set point as calculated above.

An additional way to adjust the position of the collector row is tomeasure temperature of the working fluid and moving the collector rowslightly in one direction and then the other to assess change intemperature or rate of change in temperature of the working fluid. Aworking fluid temperature offset may be calculated by finding theposition that maximizes the temperature or that maximizes thetemperature and minimizes the rate of change of temperature near theposition at which the temperature is at its maximum. This method may beused periodically to calculate a new wear offset value or a separateworking fluid temperature offset value that may be stored separatelyand/or used in conjunction with other settings as discussed above.

The control system may be localized to the central controller. In onelocal control system as illustrated in FIG. 8 and FIG. 9 (illustratingmultiple arrays, each having an individual row controller), the time,row angle, and calibration offset are calculated or stored at each rowcontroller, and little or no information or instruction is received fromother controllers. Information that might be received from othercontrollers is e.g. stow (park) the collectors by turning them to faceearth or another safe position, track the sun, lag the sun bymaintaining the collector stationary for a period of time that theapparent motion of the sun would otherwise be tracked, and defocus thecollectors by moving them off of the set point at which the collectorsobtain maximum solar energy by e.g. five degrees. In the system depictedin FIG. 8, the row controller receives information from theinclinometers of each of the rows and adjusts an individual row at atime to position the row at the desired angle. Signals indicating thetemperature of heated working fluid (in one instance, heated oil from atrough array) from each of the rows discharging heated working fluid toa common pipe are sent to a field controller via a sensor module andoptional sensor router, which communicates information about thetemperatures of each of the rows to a field controller that compares thetemperature values to established values to instruct the row controllerto stow, track, lag, or defocus. The field controller optionallyreceives information from weather sensors and/or the process utilizingthe working fluid (e.g. a power plant) to also make decisions on whethera row should stow, track, lag, or defocus.

FIG. 9 illustrates multiple arrays in which each of the row controllersoperates independently of a central controller.

The local controller will therefore calculate solar angle from latitude,longitude, time of day and date, utilize weather information directly,and perform other responses as discussed above and below for this typeof array.

All logic and controls may be provided at each local row controller.

A row controller sequentially actuates each of its associated rows asdiscussed above.

Row controllers may each comprise an enclosure; a logic board with itsmicrocontroller; a plurality of relays, each relay interfacing with thelogic board and wired to a motor of a row; and one or more powersupplies for the logic board and for the motors. Each logic boardreceives inputs such as signals representative of weather condition,inclinometer position, and/or working fluid temperature, and each logicboard uses this information along with e.g. time of day and dateinformation to calculate what action to take (e.g. move solar thermalenergy collector 1 degree; place collector row into “stow” condition,where reflector row points to ground rather to the sky) and when.

A particular control scheme is illustrated in FIG. 10. In this controlscheme, each row controller receives a command such as stow, track, lag,wash, or defocus from the field controller, and the row controller takesthe indicated action in response. While tracking, the row controllercalculates a solar angle at which to set the row. The calculated angleis compared to a minimum value and a maximum value. If the calculatedangle is less than the minimum value or greater than the maximum value,the row is placed in the stow position. If not, the row is moved to thecalculated angle, and the cycle is repeated. If the row controllerreceives a command other than the “track” command, the row controllerpositions the collector row as instructed until the row controllerreceives a different instruction from the field controller. If noinstruction is received, the collector row proceeds to a “stow”position.

The optional field controller in this instance receives signals fromvarious sensor modules to decide what instruction to send to the variousrow controllers. For instance, if weather sensors indicate that there issufficient wind and/or rain, the field controller instructs all rowcontrollers to stow their respective rows. If a wash command has beenentered by e.g. a user interface, the field controller instructsselected or all row controllers to move their respective rows to a washposition. Likewise, if the working fluid exit temperature from one ormore rows is at or above a threshold for the maximum fluid temperature,the row controller or controllers associated with those rows areinstructed to defocus that row or those rows. If the working fluidtemperature nearing the threshold for a “nearing maximum” working fluidtemperature, the particular row controller is instructed to lag theparticular row (i.e. not track the sun and remain in its presentposition) for one cycle. Otherwise, the field controller sends the rowcontrollers a signal to track the sun, and the row controllers runthrough their cycles of controlling the position of each rowindividually until an instruction to the contrary is received from thefield controller.

A distributed control system is illustrated in FIG. 11 and in FIG. 12(illustrating dedicated control wires from the central or fieldcontroller to row controllers for multiple arrays) as well as in FIG. 13(illustrating a “daisy-chain” arrangement of field controller and rowcontrollers for multiple arrays). Time and collector row angle for allrows are generated at the field controller, and an optional GPS systemprovides location data as well as a reference time signal. A rowcontroller comprising a microcontroller receives the angle set point andactuates each row individually to move the row to a desired position bycomparing the set point to the angle received from the inclinometer andactuating the row motor as needed. The microprocessor can utilize acommunication protocol such as Bacnet to directly communicate with thecentral field controls. The temperature of the working fluid from eachrow discharging to the common discharge pipe is also provided to thefield controller or to the microcontroller to adjust the position of thecollector row as described herein. Likewise, information from theprocess that uses the heated working fluid and/or weather sensors isprocessed by the field controller and/or the row controller to providechanges to set points for the various rows or directions to stow, track,lag, or defocus a row, selected rows, or all rows.

A particular control scheme for the distributed control system isillustrated in FIG. 14. In this particular control strategy, a fieldcontroller may perform the same or similar decisions as discussed above.For instance, the field controller verifies whether it has received aninstruction or information indicating that collector rows should move toa stow position, such as an operator's instruction to stow collectors orweather information indicating there is sufficient precipitation and/orwind. In this instance, the field controller may send row controllers anangle set point that the row controllers use to move collector rows tothe desired angle, effectively parking the rows. A wash command receivedby the field controller results in the field controller sending out anangle set point to row controllers to place selected or all rows to anangle appropriate to wash the collectors of the rows. If the workingfluid exit temperature is at a threshold for a maximum working fluidtemperature, the field controller may provide an angle set point to theselected row controller or controllers to effectively defocus thedesired row or rows. In one instance, the field controller uses aproportional-integral-derivative control loop to determine a targetangle offset from a calculated desired solar angle to provide acorrected angle set point to the row controller(s). In addition, if thefield controller in comparing the set point or target angle to a “stow”condition maximum or minimum value finds that the calculated angle isabove the maximum or below the minimum value, the field controller sendsselected or all row controllers target angles that effectively move thecollector rows to a stow position. Row controllers in this instancereceive target angles from the field controller and perform limitedfunctions with the target angles. A row controller may optionallycompare the target angle to maximum and minimum positions as discussedabove and stow the controller's rows as discussed above as well asoptionally send an alarm to a control panel. Alternatively, the rowcontroller may not make any adjustment to row position and may just sendan alarm signal. The row controller may then optionally compare the rowangle as provided by a row's inclinometer to a maximum acceptable and aminimum acceptable value stored locally or obtained via the networkconnecting the controllers and, if not acceptable, stop taking actionand send an alarm. Otherwise, the row controller simply controls rowposition to the set point received from the field controller asdiscussed above.

Various conditions may be measured and used as inputs to the centralcontroller. These include:

-   -   for weather:        -   Wind speed        -   Wind direction        -   Air temperature        -   Humidity        -   Precipitation        -   Cloudiness        -   Cloud factor        -   Direct normal irradiance;    -   inclinometer angle, to both reposition accurately and to assess        whether the row is stuck;    -   angle of sun or sun location (as measured by e.g. brightness or        heat or row temperature);    -   row temperature (to control to a set point, to lag, to defocus,        or, if too high, to point the row, selected rows, or all rows        away from the sun);    -   Temperature of working fluid        -   from entire array        -   from selected rows of the array        -   from each row of the array    -   Limit switch inputs to prevent collector rows from moving to        positions that would damage equipment; and    -   GPS input for very accurate time and site location

User inputs may also be accommodated by the central controller. Theseinclude:

-   -   Over-ride values for    -   Temperature set point    -   Offset    -   Shut down rows or array    -   Move to wash or maintenance position

In addition, limit switches may be used as an input to the centralcontroller or row controller to shut off power to a collector row motor,or limit switches may be used in series with relay actuator wiring tointerrupt power to the relay to stop the motor for a collector row.

Communications from sensors and among controllers may occur a number ofways. There may be dedicated cables from the central controller to eachrow controller or sensor. Alternatively, the row controllers aredaisy-chained, allowing the central controller to communicate with someor all row controllers using a single control cable. Likewise, inputssuch as working fluid temperature and inclinometer angle may bedaisy-chained with their respective cables. Communications may insteador additionally be performed using e.g. wireless mesh communications(802.15.4) or other RF protocols.

Solar Thermal Energy Collectors

The systems discussed above are well-suited to various solar thermalenergy collectors, such as trough collectors or linear Fresnel arraycollectors.

For instance, a trough collector array may be formed using solar thermalenergy collectors as described in PCT/US2009/041171, entitled “SUPPORTSTRUCTURE FOR SOLAR ENERGY COLLECTION SYSTEM”, the contents of which areincorporated by reference herein as if put forth in full below. Suchcollectors may be comparatively small when compared to previous troughcollectors used in generating process steam for e.g. power generation,air conditioning, food processing, or oil recovery from earthformations.

An aperture of a solar collector such as a trough collector may be lessthan about 2 or 3 meters.

A trough or other type of collector of an array such as the one referredto in the PCT application cited above may have a chain and sprocketdrive. Such drive is not typically considered to be sufficiently preciseto use in accurately positioning a collector. Often, more precise drivessuch as worm gear drives are used. A system as described herein mayoften utilize less precise positioning means such as chain and sprocketdrives.

Types of Solar Thermal Energy Collectors

-   -   Trough    -   Configured to rotate more than 180 deg, especially more than 200        or 220    -   Even up to 270 deg rotational configuration    -   Chain drive

If collectors are comparatively small, it is helpful to provide a moreprecise control system such as one disclosed herein. The smallerrotational mass (especially where the axis of rotation for a row islocated within the parabola defined by the mirror, such as coaxiallywith the collector tube or at the center of mass for the reflector incross-section) in combination of a more precise control system asdisclosed herein allows better control over temperature of the workingfluid exiting the array and improved efficiency in collection of solarenergy. While a more precise control system as disclosed herein may beapplied to larger solar collectors, the gains in collection efficiencyand/or temperature control may not be as large for a larger solarcollector as for a smaller solar collector.

Discussed below is a particular implementation of a controlconfiguration and strategy.

Micro Concentrated Solar Power (Micro CSP) can utilize trough solarcollectors with a parabolic shape to reflect sunlight onto an absorbertube located at the focus on the parabola. The absorber tube is filledwith a liquid that is pumped through a thermal loop, which could be usedfor solar process heating, air conditioning, or power generation, amongother uses. Rays that are directed toward the collector in parallel withthe axis of symmetry reflect to the focus of the parabola. Adjusting thecollectors to face the sun throughout the day maximizes the amount ofsun rays that are parallel to the axis of symmetry and, thus, maximizesthe amount of solar power directed to the absorber tube. Since thistechnology relies on rays parallel to the axis of symmetry, it isimportant that the collectors continually face the sun to maximize theenergy harvested in a day. The SopoTracker maximizes the solar powercollected, which is especially important to large scale solar powersolutions.

In a typical field deployment, rows of collectors are positioned so thattheir absorber tubes are oriented along a North-South line. Not onlydoes this arrangement allow efficient use of space and prevent/reducecollectors from casting shadows on neighboring collectors, but it alsoenables the collectors to change their East-West direction by simplyrotating about the absorber tube. The SopoTracker can accommodate largefields by using a system of Controllers, as explained below. However, itcan also be used for smaller applications, including a single-collectorsystem sometimes referred to as the SopoLite—for example a small-scalethermal loop that sits on a portable trailer, which can be used for datacollection. SopoTracker applications are not limited to just paraboliccollectors, but could also be applied to pyrheliometers to collectdirect measurements of solar radiation and to enhance other technologiesthat benefit from directly facing the sun, among other uses.

Advantages of the SopoTracker

Features and advantages of the SopoTracker over other solar trackers caninclude some or all of the following:

A rapid stow function that enables the collectors to return to aprotective HOME position (in which the collector faces downward or otherposition away from the sun) within seconds.

Rotates at least 270 degrees to capture as much sunlight as possible aswell as stow the collector in a safer, earth-directed position.

Built-in safety features to prevent over rotation, which could result inself-inflicted damage to the SopoTracker, the solar collector, and/or toelements in the thermal loop.

Complete solar tracking system that can control large fields in asystematic fashion and enables both large scale and specific commands(e.g., Send all collectors to the HOME position in the event of a stormor defocus a single row or even a single collector that is overheated).

Adaptable hours of operation that may be specific to the location, timeof year, etc., to capture the most sunlight for the amount of energyexpended on controlling the collectors.

Integrative system that can integrate, analyze, and respond toinformation such as time, sun angle, wind speed, weather conditions,heat generation, manual commands sent via internet, etc., to optimizesolar collection and intelligently respond by, for example, adjustingthe collectors to track the sun, defocus when too hot, or return to HOMEin a protective manner.

Data collection and transmittal, which can help assess the efficiency ofthe thermal loop or help foresee and prevent any potential problems.

Reducing the need for drive train accuracy and allowing the use of e.g.sprocket and chain drive.

Using Field Controllers and Plant Controllers for Large Fields

One approach to controlling large fields of collectors while maintainingthe specificity of control is by implementing a hierarchy ofcontrollers. For example, in one example architecture, the SopoTrackerincludes Row Controllers, Field Controller(s) and a Plant Controller.Each Row Controller maintains the tracking for a cluster of one or morerows of collectors. The Row Controller typically would be responsiblefor basic control in keeping a cluster of collectors aligned with thesun's angle. A Field Controller could facilitate communication betweenmultiple Row Controllers, a Plant Controller and the internet. Thiscommunication could, for example, utilize Ethernet hardware, includingEthernet switches or Ethernet routers. Both the Plant Controller andField Controller could, for example, run on Linux. In oneimplementation, the Plant Controller might monitor information such asweather conditions, flow rate, heat generated by each row of collectors,etc. and send commands via the Field Controller and Row Controllers tocollectors when a response to these factors is necessary. By taking incommands from the Plant Controller and the internet (i.e. sending manualcommands from afar), the Field Controller can relay commands to overridethe Row Controller's basic solar tracking to account for other factors,either as an entire field or as a single row or as a set of rows. TheField Controller can change the start and stop times for tracking sinceit is communicating with many Row Controllers. Thus, accounting fordifferent hours of operation for the changing seasons and for daylightsavings would be relatively easy. Another example of field-wide controlswould be if the weather station indicates that the amount of energy useis less than what is being generated, the Plant Controller could send acommand that the entire field of collectors should be sent to the HOMEposition to conserve energy. However, in the event that a single row ofcollectors is overheating, then the Plant Controller could send aspecific command to the affected row to return to the HOME position todefocus. The connection to the internet could also enable the FieldController to send information out to the solar field operator, to thepower generator or to others. This information could be analyzed tocalculate efficiency or to predict and/or prevent potential problems.

In one implementation, the Field Controller is an FTP server to whichfiles are written and read by both the Row Controller and the PlantController. The following lists example communications that thedifferent controllers may send to each other:

Plant Controller to Field Controller:

-   -   Home (at evening, excess wind, low sun, or some other error)    -   Start tracking (usually in morning)    -   Defocus row# (over heat)

Field Controller to Plant Controller:

-   -   Error in row#    -   Status report

Field Controller to Row Controllers:

-   -   Start    -   Defocus row#    -   Home    -   Off row#

Row Controller to Field Controller:

-   -   Report row encoder position    -   Error row#

Row Controller

In one implementation, the Row Controller can adjust multiple rows ofcollectors (a cluster) to track the sun. In a large field, many of theseRow Controllers can be used to control numerous rows, which are alsocontrolled by a Field Controller. In a smaller application, as in theSopoLite, a single Row Controller may also play the roles that the PlantController and Field Controller play in a larger field. This wouldenable the Row Controller to use weather station information,temperature measurements, etc. to determine how the collectors shouldfunction. In this section, however, the description below will providean example of how a Row Controller could be designed to meet the basicfunction of controlling rows of collectors to track the sun and receivecommands from a Field Collector.

One version of the Row Controller directs a cluster of up to six rows ofcollectors. The collector rows are rotated by a chain-sprocket apparatusthat is driven by a motor controlled by the Row Controller hardware,which includes a single board controller, power supply, motor powersupply, and driver/selector board. An encoder installed on one collectorin each row measures and encodes the row's position, which is read bythe software programmed in the single board controller. The softwarewill use an algorithm to calculate the sun's angular position and thenrotate each of the rows individually, looping through the six rowsthroughout the day, to match the calculated angle position.

The collectors in a row are connected to a crank shaft by a fewchain-sprocket apparatuses, which have a gear ratio of 9:1. Thechain-sprocket apparatus includes a chain link that wraps around an18-inch drive sprocket that connects to the end arm of the collector anda 2-inch drive sprocket that is attached to the crank shaft. The crankshaft is rotated by a ½ horsepower DC motor, which runs on a 90 volt DCpower supply activated by the Row Controller hardware. The 18-inchsprocket also has a safety feature called a limit switch. The limitswitch prevents over rotation of the collector by creating anon-conducting gap between the sprocket and a metal switch. In FIG. 4,there is a white semi-circular piece of material over the blue sprocket.This white piece prevents a metal switch from touching the sprocket. Ifthe collector over rotates, the metal switch will exceed the whitesemi-circle and will cause the switch to close. When the switch closes,an electrical signal is sent to the hardware through a RJ45 Ethernetwire. Alternatively, the limit switch may be bolted to collector panelstands, and an arm on the panel impacts the switch prior to impactingthe panel stand. The signal may be a simple voltage or lack thereof, andtherefore either presence or absence of voltage is sensed.

Each row has a encoder that detects the angle at which the collector ispositioned. The encoder communicates using e.g. a 5-volt level of RS232signal. An encoder may transmit e.g. 2 bytes of data every 10milliseconds. Data may be sent 56K, no parity, 1 stop bit, for instance.

The data format is as follows:

High ordered byte transferred first.

Bit 7 is set to 1 to indicate high order

Bit 6 to 0 are high order data

Low order byte transferred immediately after

Bit 7 is set to 0 to indicate low order

Bit 6 to 0 are low order data

A high bit indicator is used to make it easier for the receiver toidentify the bytes, which saves considerable computation anduncertainty.

After installing the encoder, the collector is placed upside down orright side up while the encoder is reset. The upside down position ofthe collector is set as the origin and 0 degrees. It is also referred toas home. A full rotation of 360 degrees is counted in 2̂14 (14 bitbinary) positions, which results in a resolution of approximately 45positions per degree.

The Row Controller hardware in this example includes a single boardcontroller, power supply, motor power supply, and driver/selector board,which enable the tracker (i.e., Row Controller) to control 6 rows ofcollectors.

The driver/selector board in this instance is a printed circuit board(PCB) and may include some or all of the following:

-   -   6 optical decoders    -   selector    -   connectors/sockets to ethernet, RS232, power    -   AC power switch    -   manual/automatic mode switch or outboard terminal        block-connection switch    -   manual motor power switch    -   manual reverse/forward switch    -   dip switch for manual row motor select    -   8 RJ45 sockets or screw terminal blocks    -   reset switch for single board computer    -   12 v and 5 v LED to indicate proper voltage.    -   Relays to select directions and row to power specific motor    -   power to single board computer    -   POD to control output level of motor power supply    -   inhibitor to disable motor power supply

One of the RJ 45 sockets may provide connection to Ethernet. Six of theRJ 45 sockets may provide power to the encoder as well as a limitswitch. Limit switches prevent collectors from moving beyond a safelimit in the event of a single-board computer or other electronicfailure. At least two limit switches may be used per row. One may beserially connected to the motor while another may be serially connectedto the relay driver. In alternate versions, limit switches connected tothe drivers may be replaced with limit switches that are connected tothe logic of the circuit.

In one implementation, the PCB has the potential to control six rows ofcollectors, and multiple Row Controllers are linked via switches toaccommodate large field size. Other versions can expand to control 10 ormore rows.

One version of the single board computer (SBC) is a picoFlash CPU with a186 compatible processor that runs on a limited version of DOS operatingsystem. Since the Field Controller could run on LINUX, other versions ofRow Controllers can use CPUs running on Linux instead of DOS to simplifycommunication between the two computers.

This specific software implementation operates in the following manner—

-   -   Execution Sequence:        -   BIOS of SBC starts and execute batch file in A: drive        -   STARTUP.BAT file in B: drive executes        -   Reset IO lines so that motor is off        -   Environment variables are set        -   Ethernet Packet Driver is loaded        -   Serial Port Driver is loaded        -   Timer interrupt TSR is loaded        -   Program to read date/time/operational commands from Field            Controller loaded.        -   CHOICE selection routine run        -   User has choice of N dos prompt or,        -   if there are no user input in few second, TRACKER software            is run    -   Tracker Software:        -   Initializes various routines        -   Places IO ports to motor off state        -   Serial Communications        -   Ethernet/FTP Communications to Field Controller        -   Reads configuration file        -   Reads date using standard C routine and compute solar day            and solar correction angle for the day        -   Initializes interrupt for millisecond time interrupt and            counter        -   Turn on watchdog timer which will automatically restart SBC            in case if it hangs    -   Loop through each row        -   Set output to select proper row of optical decoder for            serial input        -   Reset serial port        -   Wait one second        -   Reads encoder for two second and accept average as current            position        -   Compute current expected position from second from midnight            and correction.        -   Compute millisecond to turn motor on for difference between            current position of collector vs. optimal position to align            to sun (approx. 170-500 ms)        -   Turn on proper row selection relay        -   Turn on forward direction relay        -   Turn off motor power inhibitor relay (turn motor on) for            computed millisecond    -   Tracker    -   During each row or between loops for whole entity of 6 rows, Row        Controller reads and writes to FTP server in Field Controller.    -   Writes:        -   Normally report position of encoder for all rows        -   If there are stuck or error, it will report errors    -   Reads:        -   Command file containing:        -   Home all        -   Defocus row        -   Home row        -   Off row

Internally, the Row Controller program cooperatively multitasks. Thetimer counter increases in increments of approximately one millisecond.The Delay function waits for the delay counted in ms, while stillmultitasking (mainly reads serial port). The millisecond count isdivided by 1024 to approximate a second and coordinate one-secondevents. One-second events include resetting the watchdog timer,resetting the display of the raw encoder position during large movesthat are not routine mini tracking moves, and blinking of the LED.

Other Methods of Tracking and Calibration

Another method of tracking, among others, uses photovoltaic (PV) cells.PV cells produce electrical current from light, such that the amount ofelectricity generated provides a quantitative measurement of lightreceived by the PV cells. A ring of PV cells could be placed around theabsorber tube to indicate the amount of sunlight that each particularpart of the collector is reflecting toward the tube. The ring of PVcells could be grouped into the two halves of the reflector. Bymeasuring the amount of light reflected by each half of the collector,which is correlated with the amount of electricity generated by eachhalf of the PV cell ring, a SopoTracker could adjust the angle of thecollector so that both sides reflect equal amounts of sunlight.

The same ring of PV cells could be used to calibrate the SopoTracker.This would give quantitative measurements of the amount of light that isreflected onto the absorber tube.

Another method could use tubes fitted around the absorber tube toprovide pyrheliometer readings. In both instances, the quantitativemeasurement of light/radiation that is reflected onto the absorber tubecan be used to determine the angle at which the collection is at itsmaximum. By making a comparison to the sun angle position derived fromthe SopoTracker software, an offset can be determined to send a zeroposition to the encoder.

In some implementations, the functions of the Field Controller and PlantController could be integrated into a single computer that would controlplant information while also facilitating the necessary communication,regardless of the amount of collectors being used. Thus, a singleController would integrate information from the weather station,temperature readings, flow measurements, etc., and send commandsdirectly to the Row Controller.

1. A solar thermal energy collector array comprising a) a plurality ofrows of solar thermal energy collectors comprising a first solar thermalenergy collector row and a second solar thermal energy collector row, b)a plurality of electric motors comprising a first motor configured toposition the first solar thermal energy collector row and a second motorconfigured to position the second solar thermal energy collector row, c)a plurality of inclinometers comprising a first inclinometer and asecond inclinometer, the first inclinometer being coupled with the firstsolar thermal energy collector row and the second inclinometer beingcoupled with the second solar thermal energy collector row, d) a rowcontroller in communication with the plurality of electric motors andthe plurality of inclinometers, the row controller being configured tosequentially actuate i) the first motor to position the first solarthermal energy collector row according to a position of the first solarthermal energy collector row as indicated by the first inclinometer, andii) the second motor to position the second solar thermal energycollector row according to a position of the second solar thermal energycollector row as indicated by the second inclinometer.
 2. An arrayaccording to claim 1 wherein the row controller comprises afield-mounted enclosure in the immediate vicinity of the plurality ofrows.
 3. An array according to claim 1 and further comprising a centralcontroller in communication with the row controller, the row controllerbeing configured to calculate a setpoint for the row controller and thecentral controller not being configured to calculate a setpoint for therow controller.
 4. An array according to claim 3 wherein the centralcontroller is configured to provide an instruction to the row controllerto position the rows controlled by the row controller to a positionselected from a stow, track, lag, defocus, and wash position.
 5. Anarray according to claim 4 wherein the central controller is configuredto provide said instruction in response to a temperature of a workingfluid in said array.
 6. An array according to claim 4 wherein thecentral controller is configured to provide said instruction in responseto a weather sensor.
 7. An array according to claim 4 wherein thecentral controller is configured to provide said setpoint in response toa signal indicative of an operating condition of said facility thatextracts work from heated working fluid of said array.
 8. An arrayaccording to claim 1 and further comprising a central controller incommunication with the row controller, the central controller beingconfigured to provide a setpoint representative of row angle to the rowcontroller.
 9. An array according to claim 8 wherein said setpointrepresentative of row angle is sufficient to place the rows controlledby the row controller to a position selected from a stow, track, lag,defocus, and wash position.
 10. An array according to claim 9 whereinthe central controller is configured to provide said setpoint inresponse to a temperature of a working fluid in said array.
 11. An arrayaccording to claim 9 wherein the central controller is configured toprovide said setpoint in response to a weather sensor.
 12. An arrayaccording to claim 9 wherein the central controller is configured toprovide said setpoint in response to a signal indicative of an operatingcondition of said facility that extracts work from heated working fluidof said array.
 13. An array according to claim 1 wherein the pluralityof rows comprises a number of rows, said number being at least five, theplurality of electric motors comprises at least said number of motorsrespectively coupled to said rows, the plurality of inclinometerscomprises at least said number of inclinometers respectively coupled tosaid rows, and said row controller is configured to sequentially but notsimultaneously actuate any of said number of motors.
 14. An arrayaccording to claim 13 wherein said number is at least ten.
 15. An arrayaccording to claim 13 wherein said number is at least fifteen.
 16. Anarray according to claim 1 wherein the solar thermal energy collectorsare trough collectors.
 17. An array according to claim 16 wherein thetrough collectors each have a chain and sprocket drive coupling theelectric motors and the collector troughs.
 18. An array according toclaim 16 wherein the trough collectors each have an aperture less thanabout 3 meters.
 19. An array according to claim 18 wherein the apertureis less than about 2 meters.
 20. A method of positioning a plurality ofrows of a solar thermal energy trough collector array comprisingsequentially and not simultaneously positioning any of the number ofrows of the array, the number being at least two.
 21. The method ofclaim 20 wherein the number is at least five.
 22. The method of claim 20wherein the number is at least ten.
 23. A method according to claim 20wherein the rows are positioned consecutively.